Process of making phosgene



June 5, 1923.

D.B.BRADNER PROCESS OF MAKING PHOSGENE Filed Jan. 11 1922 Patented it... 5, 1923.

UNITED STATES- PATENT -oi= =1cEt; f

DONALD B. BRADNER, OF EDGEWOOD, MARYLAND.'

PROCESS OF MAKING' PHOSGENE.

Application filed January 11 1922. Serial No. 528,551.

To all whom itmay concem:

Be it known that I, DONALD B. BRADNER, a citizen of the United States, residing at Edgewood, Maryland, in the county of 6 Harford and State of Maryland, have invented certain new and useful Improve ments in the Processes of Making Phosgene, of which the following is a specification.

This invention relates to the production of i 10 phosgene and more specifically to a new process for making this substance.

Among the,objects of this invention is the production of phosgene by a simpler and more efficient method than heretofore used.

A further object of this invention comprises the production of phosgene under conditions whereby the yield approaches the theoretical quantity.

In pIIOI processes for making phosgene, chlorine was allowed to react with CO in the presence of asuitable catalyst,'such as charcoal. The reaction is'as follows:

C1 +CO=COCl By refrigeration, the phosgene produced was reduced to a liquid.

The chief difiiculty in this old process is due to the fact that it necessitates the use of CO in a very concentrated and substan- 3O tially pu're'condition. One of the common methods of obtaining this CO consisted in" first burning coke with an excess of air to form CO which was removed from theother flue gases by a solution of K CO The KHCO solution which resulted was 'then heated, the bicarbonate being decomposed with the liberation of CO and the reformation of K CO The CO was then mixed with oxygen (usually obtained by fractional separation from liquid air) and ,passed through a bed of heated coke, thereby forming substantially pure CO. The

reaction CO,+C=2CO is endothermic while the reaction O,+2C=2CO is exothermic; By proper control-of the quantities of CO and O which are added the"temperatu're can be maintained at the desired point.

In my process the carbon, in somesuitable form, such as coke, is-burned with an insuflicient supply of air, thereby obtaining 5 CO substantial y free'of CO, and oxygen,

. The higher the temperature,

but diluted with a high percentage of nitrogen. By properly carrying outthis combustion it is possible to'obtain a gas containing about 341%, volume. of CO and 66% -1nert gases, consisting prmcipally of nitrogen.

In actual operation, however, I usually obtain a gas of about 27% CO, 5% CO and 68% nitrogen. It is to be understood, however, that mixtures of gases which are not so rich in CO may be used for the subsequent steps of my process; in fact, any CO present will react, the lower limit being an economic one. i

The gas mixture resulting from this combustion is then preferably dried by a suitable dehydrating agent, such as sulphuric acid, and then mixed with the theoretical quantity of chlorine in the presence of a suitable catalyst, such as bone black, activated charcoal. or sunlight. The reaction takes place with the liberation of. considerable heat, consequently the flow of gas should be regulated to maintain the 'most eflicient temperature The following table gives the percent dissociation of phosgene at different temperatures:

Pereentaze the more rapidly "this equilibrium is reached. Conse quently a high initial temperature and alow finishing temperature will give the maximum capacity plus the highest percent conversion. I- prefer to have the reaction take place at temperatures of 200400 C.

The gas, after leaving the reactor, is passed through a chamber filled with-adsorbing material, such as silica. gel, activated illustrated, diagrammatically, an.

charcoal, etc. The adsorbent takes up the phosgene and removes same from the inert gases, such as nitrogen, carbon dioxide, etc.,

which )ass ofl? either as Waste gases or may be col ected for use where nitrogen free from oxygen is desired. The phosgene may be recovered from the adsorber either by heat, reduced pressure or both, and if liquid phosgene is desired it may be condensed by refrigeration, increased pressure. or a combination of refrigeration and higher pressure.

If silica gel is used as the adsorbing agent it is desirable to maintain same at a low temperature during the adsorption. Suitable temperatures are from O to 20 C., and very good results may be obtained by operating around 5 to 10 C. The adsorptive powers of the gel decrease with temperature, so it is better to carry out the adsorption at low temperatures for best results.

In the accompanying drawing there is arrangement of apparatus for" carrying out my process. Coke is burned in the combustion chamber #1, air being supplied at #2. The products of combustion pass out through the conduit #3 and by manipulation of the valves #4 and #5, these gases may either pass out into the air or else on to the gas holder #6. From this gas holder these combustion gases are conducted through valve #7 to a suitable drying tower #8 containing sulphuric acid or other suitable drying agent and the dried gases are then conducted throughthe valve #9 to reactor #10. The sulphuric acid enters through the valve #11 and the spent acid may .be withdrawn through the valve #12. Chlorine gas is also supplied to the reactor #10 through the valve #13 from a suitable source of chlorine. This reactor #10 contains the catalytic material. The chlorine combines Withthe C0 of the dried combustion gases While in the reactor 10, and phos'gene' is produced thereby. T e phosgene and the residual gases are swept from the reactor by the current of gas on to the adsorbers #14 containing a suitable adsorbing agent, as above described. The phosgeneis thus taken up with the adsorbent and the inert gases pass from the adsorbers and out through the valves #15 and #16, the valves #17 and #18 being closed. The valves #15 and #16 are then closed and the valves phosgene is evolved from the adsorbent ma terial and passes out through the valves #17 and #18 to a suitable condenser #19. p The adsorbers, #14, are jacketed and during ad-sorptionewhen it is desired to cool the adsorbent, cooling fluid may enter at #20 and leave 'at, #21... During the regaseous product to the action -ject ing the actlon of an adsorbent for removing the 'phosgene from the ingfWith #17 and #18 are opened and the covery step of the phosgene fromthe ad-.

sorbent, heating fluid may be supplied to the jacket at #22, and withdrawn, together with such portion as is condensed, at #23.

If it is desired to produce a vacuum in the adsorbers #14, the valves #24 and #25 are closed andv the adsorbers exhausted.

This process may be carried out either continuously or intermittently. When continuous operation is desirable it is advisable to have :1 battery of adsorbing chambers, so that when. adsorption is taking place in one chamber, the adsorbed phosgcne may be recovered from another chamber, and the latter revivified for subsequent, use.

p The present invention is not limited to 1. In a process of making phosgene, treating chlorine with a mixture of CO highly diluted by inert gas and then subjecting the gaseous product to the actionof an adsorbent for removing the phosgene from the other gases. i

2. In a process of making phosgene, treating chlorine with a mixture of CO highly diluted by inert gas and then subjecting the of silica gel at temperatures of 0 to 20 C.

- 3; In a process of making phosgene, treats ing chlorine with a mixture of CO highly diluted by inert gas, subjecting the gaseous product to the action of an adsorbent for removing the phosgc-ne from the other gases, volatilizing the phosgene from the adsorbent and then liquefying the evolved phosgene.

4. In a process of making phosgeno, treating with chlorine in the presence of a catalyz er the products resulting from burn-- ing carbon with an insuflicient amount of air for complete combustion and then subresulting gaseous product to the other gases. process of making phosgene, treatchlorine in the presence of a catalyzer at temperatures of 200-400 C, the dried products resulting from burning carbon with an insuflicient amount of air for complete combustion and then subjecting the resulting gaseous product to the .actlon of silica gel at temperatures of 5-10 C. DONALD B. BRADNER.-

Ina. 

